(CNN) -- The mother and father of missing Oregon boy Kyron Horman repeatedly urged stepmother Terri Horman to co-operate with police during a news conference Thursday.

"I really want her to do the right thing," said Kyron's mother, Desiree Young. "Kyron is still out there and needs to be home."

Court records released Thursday revealed that Kaine Horman, the boy's father, believes the stepmother is involved in Kyron's disappearance.

The revelation was made public after a restraining order against Terri Horman was unsealed by Multnomah County court authorities in Portland.

The father alleges his wife knows what happened to Kyron, who was last seen at school more than one month ago.

"I believe respondent is involved in the disappearance of my son Kyron who has been missing since June 4," Horman wrote in his request for the restraining order. "I also recently learned that respondent attempted to hire someone to murder me. The police have provided me with probable cause to believe the above two statements to be true."

The restraining order bars Terri Horman from having any contact with Kaine Horman or the couple's 20-month-old daughter.

When asked by reporters at the Thursday news conference in Beaverton, Oregon, how he processed the information discovered in the restraining order he said, "I didn't process it. It's not important right now. Kyron is still missing. He's still missing."

This is the second time in a week that the boy's biological parents pleaded with the stepmother to work with investigators. But there have not been any changes since the earlier request, said Young. "She is still not co-operating."

"I'm so angry, I don't have the words," said Young. "She is not taking an active role in trying to find Kyron. She is not telling the truth."

"I've known her for a long time, said Young, "I know she's lying."

All three adults have taken polygraph tests as the investigation into Kyron's disappearance continues, said Kaine. Terri Horman was subjected to two, but did not pass either, he said.

Young and Kaine Horman said they have been totally blindsided by the disappearance of their son and by the events that followed.

Terri Horman's lawyer could not be reached for comment later Thursday.

Lt. Mary Lindstrand said the Multnomah County Sheriff's Office had no comment on the allegations made by Kaine Horman.

Authorities have not named any suspect or person of interest in connection with Kyron's disappearance.

Asked if the department believes Kyron is alive, Lindstrand said, "We are going with the premise, that, yes, Kyron is alive and we are going to bring him home."

Relatives of Kyron have said they are trying to keep the focus on finding the boy and not suspicions about the boy's stepmother.

Kyron went missing after Terri Horman dropped him off at school on June 4. The stepmother said she last saw Kyron walking down a hallway toward his second-grade classroom at Skyline Elementary School in Portland, according to police.

Sources told CNN affiliates that investigators believe that Terri Horman has lied to them, and cell phone records could show she wasn't where she claimed to be.

Kyron's family members said they hope people will focus more on the missing boy.

"Our main goal is to keep Kyron in the front of everyone's mind because we have a better chance of finding him. So we are constantly working to keep him the focus of the story and not Terri," the family members said in an e-mail.

Terri Horman was in the headlines Monday when CNN affiliates KGW and KATU reported that she had attempted to hire a landscaper to kill her husband several months ago.

KGW reported that sources believe Terri Horman approached the landscaper, who had been working on the family's property in northwest Portland, and offered the man "a large sum of money" to kill Kaine Horman.